CAIE A-Level Biology AS 2.3 Proteins Questions
Practise CAIE AS Biology 2.3 by explaining how amino-acid sequence, protein structure and molecular interactions determine function.
- Syllabus
- 2028–2030
- Course
- Biology 9700
- Level
- AS
Exam points
- Describe amino-acid structure and R groups; explain peptide-bond formation by condensation and hydrolysis.
- Distinguish primary, secondary, tertiary and quaternary protein structures and their stabilising interactions.
- Relate hydrophobic, hydrogen, ionic and disulfide bonds to protein shape; peptide bonds link amino acids.
- Contrast generally soluble, physiological globular proteins with generally insoluble, structural fibrous proteins.
- Describe haemoglobin's two α and two β chains and haem; explain Fe2+ oxygen binding and transport.
- Relate collagen's glycine-rich triple helix, hydrogen bonds and cross-links to tensile strength in fibres.
Covered syllabus points
Question 1
Which statements about peptide bond formation are correct?
1 The bond formation occurs between a carbon of one amino acid and a nitrogen of the next amino acid after the amino acids detach from tRNA.
2 The bond formation occurs at the ribosome while the amino acids are still attached to tRNA, and is a hydrolysis reaction.
3 The bond formation is important for growth of an organism and when the bond forms, a water molecule is removed.
A
1 and 3
B
2 and 3
C
2 only
D
3 only
Question 2
Which fact about the quaternary structure of proteins is correct?
A
consists of four polypeptides
B
depends on the presence of metal ions
C
depends on the primary structure of the polypeptides
D
is made of and polypeptides
Question 3
Which row correctly identifies the weak and strong bonds in the tertiary and quaternary structure of a typical protein?
disulfide
hydrogen
hydrophobic
ionic
strong
strong
weak
weak
strong
weak
weak
weak
weak
weak
strong
strong
weak
weak
weak
strong
Question 4
Which feature explains why haemoglobin is soluble?
A
All four polypeptide chains are linked together to form a spherical molecule.
B
Each polypeptide chain folds due to interactions between hydrophobic R groups.
C
The hydrophilic R groups are arranged around the outside of the molecule.
D
The iron-containing haem group of each polypeptide chain is water soluble.
Question 5
The table shows some features of collagen and haemoglobin.
Which row is collagen?
type of protein
number of polypeptides
solubility in water
fibrous
three
insoluble
fibrous
four
soluble
globular
three
insoluble
globular
four
soluble
Question 6
Which row correctly describes haemoglobin?
iron ions can associate with oxygen, forming oxyhaemoglobin
in each chain, hydrophobic R-groups of amino acids point towards the centre of the molecule
at 50% saturation, two oxygen molecules are transported by the molecule
each chain contains a haem group of amino acids surrounding an iron ion
consists of two identical alpha chains and two identical beta chains
each chain can transport an oxygen molecule
an iron ion is present within each haem group
quaternary structure has two alpha chains and two beta chains
each molecule can transport a total of four oxygen atoms
iron ions in the molecule can bind reversibly with oxygen
in each chain, hydrophobic R-groups of amino acids surround the iron ion
each molecule can transport a total of eight oxygen atoms
Question 7
Which part of the structure of haemoglobin carries oxygen?
A
four polypeptide chains
B
haem groups
C
hydrogen bonds
D
hydrophilic R groups
Question 8
The flow chart shows some of the steps in the formation of collagen.
Which row correctly identifies X, Y and Z ?
X
Y
Z
disulfide
fibres
fibrils
hydrogen
fibrils
fibres
hydrogen
microfibrils
fibres
peptide and hydrogen
fibres
microfibrils
Question 9
Which feature of collagen enables it to fulfil a structural role in skin and in tendons?
A
Adjacent collagen molecules are linked by ester bonds.
B
Collagen fibres form layers with the fibres in different directions.
C
Collagen molecules are formed as a triple helix of polypeptide chains.
D
Polypeptide chains of collagen are tightly folded into compact shapes.
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